CN105115939A - Tapered multimode interference-based high-sensitivity optical fiber methane sensing device - Google Patents

Abstract

The invention discloses a tapered multimode interference-based high-sensitivity optical fiber methane sensing device. The device comprises a broadband light source, a STMS-structure tapered multimode porous sensitive film-coated optical fiber sensing device, a testing air chamber, a switch valve, a mass flow controller, a spectrum analyzer and a computer. The STMS-structure optical fiber sensing device is prepared by single-mode optical fiber-multimode optical fiber-single-mode optical fiber melting connection and then multimode optical fiber tapering. The outer surface of the tapered multimode optical fiber is pre-treated by a silane coupling agent. The sensitive film is a cage molecule A-containing alpha-hydro-omega-hydroxy-polydimethylsiloxane porous methane-sensitive film. When methane gas to be detected reacts with the porous methane-sensitive film, a sensitive film refractive index is fast changed so that sensor interference spectrum characteristic wavelength lambda c is moved. Through analysis of interference spectrum characteristic wavelength movement amount delta lambda c before and after contact between the sensor and methane gas, a concentration of methane to be detected is obtained. The device has the characteristics of high sensitivity, fast response speed, good selectivity and good stability.

Description

A kind of high sensitivity optical fiber methane sensing device of interfering based on tapered multimode

Technical field

The invention belongs to technical field of optical fiber sensing, be specifically related to a kind of the high sensitivity optical fiber methane method for sensing and the device that obtain the tapered multimode interference of methane concentration.

Background technology

Along with the fast development of optical fiber sensing technology, fiber gas sensor research is subject to extensive concern, because of its have good, the anti-strong electromagnetic of electrical insulating property, explosion-proof, can the feature such as long-term on-line measurement and be suitable for flammable explosive gas in rugged surroundings and monitor at a distance.

Single-mode fiber (SMF)-tapered multimode fiber (TMMF)-single-mode fiber (SMF) structure (STMS) is a kind of optical fiber structure based on tapered multimode fiber mode-interference mechanism, and it draws cone to form multimode optical fiber after being embedded into a segment standard single-mode fiber by one section of multimode optical fiber.This Fibre Optical Sensor based on conical fiber multiple-mode interfence has that structure is simple, with low cost, sensitivity comparatively advantages of higher, overcomes the impact of light wave strength fluctuation, can be used in the infomation detection such as humidity, hydrogen, ammonia, oxygen by wavelength-modulated.At present, researchist successively have developed the Fibre Optical Sensor of different STMS structure.[China Measures Institute's master thesis such as Wang Xueping, 2014.3.1] a kind of tapered fiber humidity sensor of coating polyethylene alcohol (PVA) film is proposed, its humidity sensing film is applied by multimode optical fiber conical region and forms in 5%PVA aqueous solution, the refractive index of humidity sensing film can change with the change of external environment humidity, obtaining humidity information according to optical power change, is 0.251dB/%RH in humidity 35 ~ 90%RH scope inner sensor peak response.(SensorsandActuatorsB, 2005,110:23 ~ 27 such as JoelVillatoro; IEEESensorsJournal, 2003,3 (4): 533 ~ 537) palladium is coated to draws cone multimode optical fiber surface to form high sensitivity hydrogen gas sensor, detectability 0.3%, 90 seconds response times.(the SensorsandActuatorsB such as DavidMonz ó nHern á ndez, 2010,151:219 ~ 222) then drawn by optical fiber cone to 5-10 μm and with 0.1 dust/second plated with palladium, golden film to form the Fibre Optical Sensor that can detect hydrogen fast, 2 seconds its response times.Monocrystalline palladium nanometer wire is also coated on the zone of action of tapered optical fiber sensors by FuxingGu etc. (AdvancedOpticalMaterials, 2014,2:189 ~ 196), and the detection limit of palladium nanometer wire to hydrogen is low to moderate 0.2%.(the OpticsCommunications such as D.RitheshRaj, 2015,340:86 ~ 92) nano-Ag particles, polyvinylpyrrolidone and polyvinyl acetate (PVA) be coated on and draw cone plastic optical fiber surface, evaluate the system of different Nano Silver massfraction (1.6,3.3 and 6.6%) to ammonia selectivity.(the OpticsExpress such as S.A.Ibrahim, 2015,23 (3): 2837-2845) then apply polyaniline nano fiber to tapered multimode fiber sensitive zones to form ammonia gas sensor, respond and be respectively 2.27 release time, 9.73min, reappearance and good reversibility.(the AnalyticalLetters such as RenataJarzebinska, 2012,45 (10): 1297 ~ 1309) proposition electrostatic self-assembled four-(4-sulfophenyl) porphyrin (TSPP) and PAH (PAH) alternating layer form ammonia gas sensor to conical fiber surface, its beam waist diameter 10 μm, 100 seconds response times, 240 seconds release times.(the SensorsandActuatorsB such as C.Pulido, 2013,184:64 ~ 69) propose by fluorophore embed draw cone polymer optical fiber formed fiber optic oxygen sensor, the fluorescent quenching signal utilizing oxygen to cause to measure oxygen content, 28 seconds response times.(the PhysiologicalMeasurement such as RongshengChen, 2013,34:N71 ~ N81) also set up one can human body breathe Fibre Optical Sensor system, its principle is that the fluorophore being mixed with polymkeric substance is coated on tapered fiber surface, oxygen has Fluorescence Quenching Characteristics, 150 seconds sensor response times, the respiratory rate of 60 times per minute can be monitored.Chen Daru etc. (ZL201110311888.7) disclose the Bragg grating hydraulic sensing method based on conical fiber, sensor-based system comprises the Bragg grating of wideband light source, photo-coupler, spectroanalysis instrument and conical fiber, when the Bragg grating of conical fiber is placed in hydraulic environment to be measured, obtain by measuring conical fiber Bragg grating centre wavelength amount of movement the hydraulic pressure be applied on Bragg grating.

Methane is mine gas principal ingredient (accounting for 83 ~ 89%), is the emphasis of mining safety monitoring.Cage molecule compound (Cryptophanes) is unique new function molecule methane to the response of direct photaesthesia found so far, the optical fiber methane sensitive film sensor forming high selectivity can be combined with optical fiber sensing technology, as methane transducer (SensorsandActuatorsB such as evanescent wave type, Fluoroscopic type, mode filtered light type, long period fiber grating type, photonic crystal fiber types, 2005,107 (1): 32 ~ 39; AnalyticaChimicaActa, 2009,633 (2): 238 ~ 243; ChineseOpticsLetters, 2010,8 (5): 482 ~ 484; OpticsExpress, 2011,19 (15): 14696 ~ 14706).Analysis shows, cage molecule A or E is mainly incorporated in polysiloxane or styrene-acrylonitrile material by current research work, and is coated in PCS plastic-clad silica fibre core, fiber core mismatch type optical fiber or long period fiber grating and forms methane optical fiber sensor.But, the sensitive thin film of these methods derives to apply after cage molecule mixes polysiloxane, styrene-acrylonitrile resin and forms, major part cage molecule is wrapped in membraneous material, easily occur that methane molecule migration resistance in these membraneous materials is large and contact the problems such as difficulty with cage molecule, (2 ~ 5 minutes), sensitivity are lower comparatively slowly to make the response speed of sensor.

Visible, all there is common problem in above technology, and namely cage molecule is not directly be exposed in methane gas, affects the ability of cage molecule response methane molecule thus, make transducer sensitivity lower, is necessary to change sensitive thin film structure.

Summary of the invention:

In order to solve above prior art Problems existing, the present invention proposes a kind of multi-mode interference-type optical fiber methane method for sensing and device of highly sensitive, fast response time, its sensing process is using the alpha-hydro-omega-hydroxy-poly dimethyl siloxane porous membrane containing cage molecule A as methane sensitive material, be coated on the tapered multimode fiber sensitive zones of SMF-TMMF-SMF structure, can realize detecting methane gas high response speed, high sensitivity, high selectivity.

For achieving the above object, the technical solution used in the present invention is as follows:

Based on the high sensitivity optical fiber methane sensing device that tapered multimode is interfered, comprise wideband light source, single-mode fiber, SMF-TMMF-SMF structure TMMF apply the formation such as the methane optical fiber sensor of porous sensitive thin film, test air chamber, controlled valve, mass flow controller, spectroanalysis instrument and computing machine.Described multimode optical fiber MMF two ends are also drawn to bore to multimode optical fiber further with single-mode fiber SMF welding respectively and are formed SMF-TMMF-SMF structure afterwards, and the two ends single-mode fiber SMF be connected with TMMF is connected respectively to wideband light source, spectroanalysis instrument and computing machine; Fibre Optical Sensor is positioned at test air chamber, and test air chamber has the air intake opening and gas outlet that pass into methane gas to be measured, and air intake opening is by the mass flow controller of controlled valve connection control methane gas to be measured.The tapered multimode fiber outside surface of described SMF-TMMF-SMF structured optical fiber sensor first adopts the pre-service of silane coupling agent aqueous solution to apply methane sensitive thin film again.

Described methane sensitive thin film is the alpha-hydro-omega-hydroxy-poly dimethyl siloxane porous methane sensitive thin film containing cage molecule A, first by optical grade alpha-hydro-omega-hydroxy-poly dimethyl siloxane, cage molecule A, pore-foaming agent ammonium bicarbonate is placed in methylene chloride and methanol mixed solvent, ultrasonicly further after stirring 0.5 hour with 2000 revs/min of rotating speeds to mix, then lift is coated on tapered multimode fiber sensitive zones automatically, methylene chloride and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium bicarbonate in film is deviate under temperature 90 DEG C and vacuum tightness 0.08MPa condition, make the methane sensitive thin film porous of formation, porosity is 12 ~ 15%, reagent dosage is respectively cage molecule A600 μm ol, optical grade alpha-hydro-omega-hydroxy-poly dimethyl siloxane 1g, the methylene chloride of pore-foaming agent ammonium bicarbonate 0.1g, volume ratio 5:1 and methanol mixed solvent 12mL.

The sensitive thin film porous that cage molecule and optical resin are mixed to form by the present invention, realize dense film by the pore-foaming agent in thermal decomposition sensitive thin film and change to perforated membrane, sensitive thin film has higher porosity, and the cage molecule quantity exposed in film significantly improves; Simultaneously, also sensitive thin film is coated to tapered multimode fiber surface and porous, after utilizing methane molecule to diffuse into porous sensitive thin film, refractive index Rapid Variable Design causes sensor transmission interference spectrum signature wavelength to move, when the porous methane sensitive thin film effect of methane gas to be measured and tapered multimode fiber outside surface, sensitive thin film refractive index changes fast, sensor interferometer spectrum signature wavelength is moved, can realize objects such as methane gas high sensitivity, high response speed, high selectivity detections.

Described multimode optical fiber draws the front diameter 125 μm of cone, draws the rear beam waist diameter D of cone to be 25 ~ 35 μm.

Described tapered multimode fiber (sensitive zones) length is L, wherein draws cone length L _tbe 0.55 ~ 0.85mm; Coating methane sensitive membrane is to conical fiber surface and porous, and porosity 12 ~ 15%, methane sensitive membrane variations in refractive index can appreciable impact transmission interference spectrum signature wavelength amount of movement, improves transducer sensitivity.

Described tapered multimode fiber outside surface adopts the aqueous solution of KH-550 silane coupling agent (gamma-aminopropyl-triethoxy-silane) to carry out pre-service, volumetric concentration is 0.1%, 10 seconds processing times, to form silane coupling agent nanometer coat, thickness is only nanoscale, for improving the adhesion of methane sensitive membrane and fiber outer surface.

Described porous polymer sensitive thin film is the alpha-hydro-omega-hydroxy-poly dimethyl siloxane methane sensitive thin film containing cage molecule A, this sensitive thin film only has response to methane gas, to non-methane class gases such as oxygen, nitrogen, carbon dioxide, carbon monoxide, sulfuretted hydrogen almost without response, selectivity is good.

The described alpha-hydro-omega-hydroxy-poly dimethyl siloxane methane sensitive thin film containing cage molecule A is low-refraction sensitive material, refractive index about 1.41, good toughness.

Described wideband light source adopts the DL-CS5014A superradiance wideband light source SLD of centre wavelength 1550nm, bandwidth 40nm.

Described spectroanalysis instrument is the Agilent86140B spectroanalysis instrument of 600 ~ 1700nm wavelength coverage.

Described sensor transmission interference spectrum signature wavelength amount of movement Δ λ _cfor after sensor contacts methane gas, contact front m level interference peaks characteristic wavelength difference.

The principle of work of this sensing device is as follows:

As basic mode LP ₀₁incident light when to enter length through SMF/ tapered multimode fiber (TMMF) welding interface be in the TMMF of L by single-mode fiber (SMF), multiple higher order mode LP will be excited in TMMF _0m, these patterns will propagate into a tight waist with different propagation constant along TMMF, arrive TMMF and output terminal SMF welding interface further, interfere reenter SMF with basic mode.For the LP be excited _0mhigh-order mode, electric field component is expressed as:

$E(r,z)=\underset{m=1}{\overset{M}{\Σ}}{c}_m{E}_m\left(r\right)\exp \left({\mathrm{i\β}}_{m}z\right)---\left(1\right)$

Wherein E _m(r) and β _mfor the propagation constant of Electric Field Distribution and longitudinal m rank pattern, c _mfor the LP of SMF ₀₁mode excitation is to the LP of TMMF _0mimitate rate, can be expressed as:

$c_m=\frac{{\∫}_0^{\mathrm{\∞}}{E}_s\left(r\right)E_m\left(r\right)rdr}{\sqrt{{\∫}_0^{\mathrm{\∞}}{\left|E_s\left(r\right)\right|}^{2}rdr{\∫}_0^{\mathrm{\∞}}{\left|E_m\left(r\right)\right|}^{2}rdr}}---\left(2\right)$

Wherein, E _sr LP that () is SMF ₀₁mode distributions.

LP in TMMF _0mpower height and the coupling coefficient η of high-order mode _mclosely related, η _mexpression is η _mshow LP more greatly _0mmould has higher power.Weak lead approximate condition under, the longitudinal propagation constant difference of the higher order mode in TMMF can be expressed as:

${\mathrm{\β}}_m-{\mathrm{\β}}_n=\frac{{\mathrm{\μ}}_m^2-{\mathrm{\μ}}_n^2}{2{\mathrm{ka}}^2{n}_T}---\left(3\right)$

Wherein: μ _m=π (m-1/4) and μ _n=π (n-1/4) is the root of zero Bessel function; n _tbe TMMF refractive index, a is that multimode optical fiber is girdled the waist radius, and k=2 π/λ is the wave number of incident light, and footnote m and n correspond to the different mode of light, m rank mould and n rank mould.The phase differential that the light of these two patterns propagates into z place is Δ φ _mn=(β _m-β _n) z.When sensitive zones length is L, phase differential when light propagates into exit end TMMF/SMF interface is:

${\mathrm{\Δ\φ}}_{mn}=({\mathrm{\β}}_m-{\mathrm{\β}}_n)L=\frac{\mathrm{\λ}({\mathrm{\μ}}_m^2-{\mathrm{\μ}}_n^2)}{4{\mathrm{\πa}}^2{n}_T}\·L=N\mathrm{\π}---\left(4\right)$

From formula (4), the distance light travels arriving SMF is L, and the light of these different modes interferes because phase place is different, occurs interfering enhancing and interference to weaken, have characteristic peak (crest, trough) in interference spectum, corresponding characteristic wavelength meets

${\mathrm{\λ}}_c=\frac{8n_{co}{a}^{2}N}{(m-n)\[2(m+n)-1\]L}(m>n)---\left(5\right)$

In formula: L is TMMF length; N is positive integer.

When the porous sensitive membrane being coated on TMMF outside surface contacts with methane gas, its refractive index will occur to change fast, make the Eigenvalue and eigenmode changes in distribution of light in TMMF, cause interference spectum characteristic wavelength λ _cbe moved.According to characteristic wavelength amount of movement Δ λ _csize, can calculate concentration of methane gas to be measured.

The present invention has highly sensitive, the feature such as fast response time, selectivity and good stability, and concrete advantage is as follows:

1. the direct welding multimode optical fiber of the present invention and single-mode fiber SMF-28, then multimode optical fiber is drawn the tapered optical fiber of taper, the light of transmission in multimode optical fiber fibre core can be made more to enter conical fiber/sensitive thin film interface in taper place and to form evanescent wave, drastically increase the sensitivity of sensor, detection limit.

2. the present invention proposes the object being realized exposed cage molecule by methane sensitive thin film porous, can solve the object such as transducer sensitivity and response speed raising preferably by controlling sensitive thin film porosity 12 ~ 15%.It is selected raw material, and adopt most suitable process conditions, the methane sensitive membrane solution adopted is formed by cage molecule A, optical grade alpha-hydro-omega-hydroxy-poly dimethyl siloxane, pore-foaming agent ammonium bicarbonate, methylene chloride and methanol mixed solvent high-speed stirred and ultrasonic process, dissolution homogeneity, viscosity easily regulates; Under temperature 90 DEG C and vacuum tightness 0.08MPa condition, deviate from methylene chloride and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium bicarbonate in film, thus make methane sensitive thin film porous, raising sensor response speed.

3. the methane sensitive membrane that the present invention adopts is made up of cage molecule A, optical grade alpha-hydro-omega-hydroxy-poly dimethyl siloxane, make full use of hydroxyl (-OH) in alpha-hydro-omega-hydroxy-poly dimethyl siloxane molecular structure can with oxygen atom generation coordination in cage molecule A structure, than the methane sensitive membrane (SensorsandActuatorsB that traditional cage molecule A and polysiloxane, styrene-acrylonitrile resin etc. are formed, 2005,107 (1): 32 ~ 39; AnalyticaChimicaActa, 2009,633 (2): 238 ~ 243; ZL200710093035.4; ZL201010593704.6) evenly, stable, film quality is higher.

4. in order to strengthen the adhesion on methane sensitive membrane and tapered multimode fiber surface, propose conical fiber surface and carry out the pre-service of gamma-aminopropyl-triethoxy-silane coupling agent, by the silicon oxygen bond (Si-O-) of the hydroxyl (-OH) on conical fiber surface and silane coupling agent, interact respectively between silicon oxygen bond (Si-O-) and the hydroxyl (-OH) of alpha-hydro-omega-hydroxy-poly dimethyl siloxane, form nano level coat, realize the object that methane sensitive membrane strengthens at conical fiber surface adhesion force.

Accompanying drawing explanation

Fig. 1 is the optical fiber methane sensing device structural representation that the present invention is based on tapered multimode interference.

Fig. 2 is based on the transmission-type methane optical fiber sensor structural representation that tapered multimode is interfered in Fig. 1.

Embodiment

Below in conjunction with accompanying drawing 1 and Fig. 2, the present invention is described in further details:

See Fig. 1, the optical fiber methane sensing device structure of interfering based on tapered multimode is linked together at two ends and the single-mode fiber SMF-28 of the conical fiber methane transducer 2 of the alpha-hydro-omega-hydroxy-poly dimethyl siloxane sensitive thin film containing cage molecule A, and it is interior and seal sensor 2 to be assembled to sensing device test air chamber 3.Adopt superradiance wideband light source SLD1 to be connected to the input end of sensor 2, sensor 2 output terminal connects Agilent86140B spectroanalysis instrument 4, and this spectroanalysis instrument 4 is connected with computing machine 6 by gpib interface connecting line 5.Air intake opening 7 and gas outlet 8 that test air chamber 3 has one to pass into pass-out methane gas 11 to be measured respectively, air intake opening 7 is connected by the mass flow controller 10 of controlled valve 9 with control methane gas 11 to be measured.

See Fig. 2, conical fiber methane transducer 2 includes SMF-28 single-mode fiber 21, tapered multimode fiber 22, methane sensitive thin film 23.Making sensor need by multimode optical fiber two ends and single-mode fiber welding, and adopt and draw cone machine that multimode optical fiber drawing is become pyramidal structure, tapered multimode fiber (sensitive zones) length is L, wherein draws cone length L _tbe 0.55 ~ 0.85mm, beam waist diameter D is 25 ~ 35 μm.The coating of tapered multimode fiber surface is automatic czochralski method containing the method for the alpha-hydro-omega-hydroxy-poly dimethyl siloxane sensitive thin film of cage molecule A, ammonium bicarbonate; Sensor after film deviates from methylene chloride and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium bicarbonate under temperature 90 DEG C, vacuum tightness 0.08MPa condition, makes methane sensitive thin film porous, porosity 12 ~ 15%.Multimode optical fiber is ThorlabsAFS105/125Y graded index MMF (core diameter 105 μm, cladding diameter 125 μm), length 42mm; Single-mode fiber adopts healthy and free from worry SMF-28 optical fiber, its core diameter about 9 μm, cladding diameter 125 μm.

Preparation process based on the methane optical fiber sensor of tapered multimode interference comprises welding and forms SMF-MMF-SMF structure, draws taper to become SMF-TMMF-SMF structure, TMMF conical region to apply methane sensitive membrane and methane sensitive membrane porous:

(1) two section single-mould fiber SMF-28 and section multimode optical fiber MMF (cladding diameter is 125 μm) is got respectively, optical fiber wire-stripping pliers are adopted to remove the coat of this two types optical fiber, flat end face is formed with optical fiber cutter cutting with after washes of absolute alcohol, through the welding of optical fiber splicer automatic mode, cutting MMF makes its length be 42mm, forms SMF-MMF-SMF structure.

(2) optical fiber welding being formed SMF-MMF-SMF structure is placed on fused conic clinker, CO ₂laser instrument, at 10.6 μm of place power 30W, makes heating region be positioned in the middle of MMF by three-dimensional adjustable shelf.Regulate CO ₂laser power 15W, by zinc selenide (ZnSe) lens pillar control CO ₂lasing beam diameter 150 μm, the melting of MMF heating region is also stretched by the upper 3 grams of counterweight constant-tensions of SMF be connected with MMF, can be formed and draw cone length L _tbe 0.55 ~ 0.85mm, beam waist diameter D is the SMF-TMMF-SMF structure conical fiber of 25 ~ 35 μm.

(3) immersed by the conical region of SMF-TMMF-SMF structure conical fiber in the aqueous solution of mass ratio 0.1% neopelex, 5% NaOH, temperature 60 C, 30 minutes time, distilled water cleans; By room temperature alligatoring in the conical region of oil removing degreasing immersion volume ratio 20% hydrofluoric acid aqueous solution 5 minutes, thoroughly clean with distilled water after taking-up; To immerse in the aqueous solution of volume ratio 0.1%KH-550 silane coupling agent 10 seconds, nanoscale silane coupling agent coat can be formed at fiber outer surface, significantly can improve methane sensitive membrane and optical fiber surface adhesion.

(4) the coating liquid preparation of responsive methane, get cage molecule A600 μm ol, optical grade alpha-hydro-omega-hydroxy-poly dimethyl siloxane 1g (molecular weight 4200, density 0.98g/mL, refractive index 1.41), ammonium bicarbonate pore-foaming agent 0.1g, methylene chloride and methanol mixed solvent (volume ratio 5:1) 12mL, stir 30 minutes with high speed agitator, stirring rate 2000 revs/min, further ultrasonic mix after, form homogeneous transparent solution.

(5) the SMF-TMMF-SMF structure conical fiber of silane coating coupling agent is placed on automatic pulling machine, TMMF is immersed in the coating liquid of responsive methane, (time of repose 3 minutes in automatic mode, pull rate 10 ~ 30 lis ms/h) adopt automatic pulling machine to lift the methane sensitive thin film forming uniform thickness 0.2 ~ 0.5 μm, last temperature 90 DEG C, vacuum tightness 0.08MPa, methylene chloride and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium bicarbonate in film is deviate under 1 hour time condition, make methane sensitive thin film porous, porosity 12 ~ 15%.

The methane optical fiber sensor of the SMF-TMMF-SMF structure of coating methane sensitive thin film is assemblied in test air chamber.When methane gas to be measured enters through mass flow controller, test air inlet of air chamber and has an effect with the porous methane sensitive thin film on TMMF surface, sensitive membrane refractive index changes fast; And the change of sensitive membrane refractive index, directly will change sensor transmission interference spectrum signature wavelength X _c.Adopt spectroanalysis instrument to detect the situation of movement of interference spectum characteristic wavelength, analyte sensors contacts front and back interference spectum characteristic wavelength amount of movement Δ λ with methane gas _c, concentration of methane gas to be measured can be obtained.

Embodiment 1: one section of multimode optical fiber MMF and two section single-mould fiber SMF-28 weldings are formed SMF-MMF-SMF structure, multimode optical fiber length 42mm, multimode optical fiber draws the rear conical region 0.68mm of cone, beam waist diameter 30 μm; After conical region precoating surfaces silane coupling agent nanometer overlayer, then along conical fiber surface coating thickness be 350nm containing the alpha-hydro-omega-hydroxy-poly dimethyl siloxane methane sensitive thin film of cage molecule A and porous.Be that the Standard Gas of Methane of 0 ~ 3.5% (v/v) is for object with concentration, have an effect with the sensitive thin film of optical fiber surface respectively, transmission interference spectrum signature wavelength increases with concentration of methane gas and moves to short wavelength direction, and trough characteristic wavelength amount of movement Δ λ near transmission interference spectrum 1550nm _clinearly relevant between methane concentration c, its equation of linear regression is:

Δλ _c＝kc+b

In formula, c is concentration of methane gas to be measured, Δ λ _cfor sensor transmission interference spectrum trough characteristic wavelength amount of movement, k is slope, and b is intercept.

Concentration known is adopted to be that the Standard Gas of Methane of 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v) detects respectively in experiment.For some methane concentrations, according to the change of transmission interference spectrum trough characteristic wavelength, methane gas can be obtained and pass into front and back wavelength amount of movement Δ λ _c, the transmission interference spectrum trough characteristic wavelength amount of movement Δ λ of corresponding variable concentrations gas calibrating gas _cbe respectively 0,0.40,0.80,1.20,1.60,1.90,2.40,2.92,3.30nm, its equation of linear regression is: Δ λ _c=0.8825c+0.2307, coefficient R ²=0.9903, namely in equation of linear regression, k, b are respectively 0.8825,0.2307.

When after methane gas to be measured and this sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λ _cfor 1.82nm, concentration of methane gas c=1.80% to be measured can be calculated, 41 seconds its response times, 43 seconds release times.

Embodiment 2: experiment adopts conical region 0.55mm, the conical fiber methane transducer of beam waist diameter 25 μm, sensitive membrane thickness 380nm, and detect with the Standard Gas of Methane that concentration known is 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v), corresponding transmission interference spectrum trough characteristic wavelength increases with concentration of methane gas and moves to short wavelength direction, its interference spectum trough characteristic wavelength amount of movement Δ λ _cbe respectively 0,0.42,0.82,1.24,1.62,2.02,2.48,3.02,3.48nm, equation of linear regression is: Δ λ _c=0.9246c+0.2293, coefficient R ²=0.9916, namely in equation of linear regression, k, b are respectively 0.9242,0.2293.

When after methane gas to be measured and this sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λ _cfor 1.54nm, concentration of methane gas c=1.42% to be measured can be calculated, 36 seconds its response times, desorption time 38 seconds.

Embodiment 3: adopt conical region 0.76mm, the conical fiber methane transducer of beam waist diameter 32 μm, sensitive membrane thickness 330nm, and detect with the Standard Gas of Methane that concentration known is 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v), corresponding transmission interference spectrum trough characteristic wavelength increases with concentration of methane gas and moves to short wavelength direction, its interference spectum trough characteristic wavelength amount of movement Δ λ _cbe respectively 0,0.42,0.88,1.24,1.72,2.16,2.32,3.04,3.46nm, equation of linear regression is: Δ λ _c=0.9115c+0.2654, coefficient R ²=0.9846, namely in equation of linear regression, k, b are respectively 0.9115,0.2654.

When after methane gas to be measured and this sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λ _cfor 3.18nm, concentration of methane gas c=3.20% to be measured can be calculated, 39 seconds its response times, desorption time 43 seconds.

Embodiment 4: adopt conical region 0.85mm, the conical fiber methane transducer of beam waist diameter 35 μm, sensitive membrane thickness 430nm, and detect with the Standard Gas of Methane that concentration known is 0,0.1,0.5,1.0,1.5,2.0,2.5,3.0,3.5% (v/v), corresponding transmission interference spectrum trough characteristic wavelength increases with concentration of methane gas and moves to short wavelength direction, its interference spectum trough characteristic wavelength amount of movement Δ λ _cbe respectively 0,0.48,0.88,1.26,1.82,2.28,2.32,3.26,3.58nm, equation of linear regression is: Δ λ _c=0.9496c+0.2767, coefficient R ²=0.9783, namely in equation of linear regression, k, b are respectively 0.9496,0.2767.

When after methane gas to be measured and this sensor contacts, transmission interference spectrum trough characteristic wavelength amount of movement Δ λ _cfor 0.96nm, concentration of methane gas c=0.72% to be measured can be calculated, 32 seconds its response times, desorption time 35 seconds.

Claims (4)

1., based on the high sensitivity optical fiber methane sensing device that tapered multimode is interfered, comprise wideband light source, methane optical fiber sensor, test air chamber, controlled valve, mass flow controller, spectroanalysis instrument and computing machine; Described wideband light source connecting fiber methane transducer, the interference signal of methane optical fiber sensor connects spectroanalysis instrument and computing machine through single-mode fiber; Described methane optical fiber sensor is positioned at test air chamber, and test air chamber has the air intake opening and gas outlet that pass into methane gas to be measured, and air intake opening is by the mass flow controller of controlled valve connection control methane gas to be measured;

It is characterized in that: described methane optical fiber sensor draws cone to form to multimode optical fiber by after multimode optical fiber two ends welding single-mode fiber further;

Described multimode optical fiber draws cone length L _tbe 0.55 ~ 0.85mm, beam waist diameter D is 25 ~ 35 μm; Tapered multimode fiber outside surface adopts the pre-service of KH-550 silane coupling agent aqueous solution to form silane coupling agent nanometer coat, KH-550 silane coupling agent aqueous liquid volume concentrations is 0.1%, 10 seconds processing times, coat thickness is nanoscale, apply porous methane sensitive thin film again, improve methane sensitive membrane and tapered multimode fiber outside surface adhesion; Described porous methane sensitive thin film is the alpha-hydro-omega-hydroxy-poly dimethyl siloxane porous methane sensitive thin film containing cage molecule A, its thickness 200 ~ 300nm; Described porous methane sensitive thin film first optical grade alpha-hydro-omega-hydroxy-poly dimethyl siloxane, cage molecule A, pore-foaming agent ammonium bicarbonate is placed in methylene chloride and methanol mixed solvent, ultrasonicly further after stirring 0.5 hour with 2000 revs/min of rotating speeds to mix, then lift is coated on tapered multimode fiber sensitive zones automatically, methylene chloride and methanol mixed solvent and thermal decomposition pore-foaming agent ammonium bicarbonate in film is deviate under temperature 90 DEG C and vacuum tightness 0.08MPa condition, make the methane sensitive thin film porous of formation, porosity is 12 ~ 15%; Reagent dosage is respectively cage molecule A600 μm ol, optical grade alpha-hydro-omega-hydroxy-poly dimethyl siloxane 1g, the methylene chloride of pore-foaming agent ammonium bicarbonate 0.1g, volume ratio 5:1 and methanol mixed solvent 12mL;

Described wideband light source adopts the superradiance wideband light source SLD of centre wavelength 1550nm, bandwidth 40nm.

2. high sensitivity optical fiber methane sensing device of interfering based on tapered multimode according to claim 1, it is characterized in that: the described alpha-hydro-omega-hydroxy-poly dimethyl siloxane methane sensitive thin film containing cage molecule A is low-refraction porous sensitive material, refractive index about 1.41, porosity 12 ~ 15%.

3. according to claim 1 and 2 based on tapered multimode interfere high sensitivity optical fiber methane sensing device, it is characterized in that: described multimode optical fiber two ends all with single-mode fiber SMF-28 welding.

4. high sensitivity optical fiber methane sensing device of interfering based on tapered multimode according to claim 1 and 2, is characterized in that: described spectroanalysis instrument is the spectroanalysis instrument of 600 ~ 1700nm wavelength coverage.